1. Field of the Invention
The present invention relates to a vector-signal processing circuit for converting vector signals composed of a plurality of analog signals to absolute values, there by processing the vector signals.
2. Related Art
Conventionally, the following three methods are generally known as methods for converting vector signals individually formed of very small analog signals of sensors, transducers, and the like to absolute values, thereby generating digital signals of TTL and the like corresponding to input signals of, for example, microcomputers:
(a) a method that amplifies the signals by using operational amplifiers, then performs analog-digital conversion for the amplified signals, and then converts the conversion outputs to absolute values by using a microcomputer, thereby generating digital signals;
(b) a method that amplifies the signals by using operational amplifiers, and then generates digital signals by using a microcomputer having analog-digital-conversion inputs; and
(c) a method that amplifies the signals by using operational amplifiers, then processes the outputs in absolute-value circuits that use ideal diodes and that are formed of two operational amplifiers, and then performs digital conversion for the outputs by using a comparator, thereby generating digital signals.
Gas meters for a city gas, for example, contain a seismoscope that functions to prevent gas leakage in the case of an earthquake. They also contain a system in which, in the case of an earthquake, an acceleration sensor senses the quake, and a valve is automatically shut. However, difficulty arises in securing the power supply for driving electrical circuits provided in such outdoor-use apparatuses as gas meters. Because of this difficulty, most of such apparatuses are configured so as to contain a battery for driving electric circuits. Therefore, techniques are being developed so that power consumption for use of these apparatuses is reduced as much as possible, and service life of the battery is increased as long as possible.
From these viewpoints, the above-described three methods have problems. Methods (a) and (b) require analog-digital converters and/or microcomputers, and method (c) requires many operational amplifiers. Therefore, any one of the methods requires a relatively high consumption current, for example, 10 xcexcA, which inhibits further reduction in power consumption.
For example, to perform an operation according to method (c), each of the absolute-value circuits using the ideal diodes requires two operational amplifiers. It also requires an adder circuit to be provided upstream of the comparator. Thus, method (c) uses many operational amplifiers.
Ordinarily, to perform high-accuracy detection of the acceleration rate from outputs of an acceleration sensor, analog signals, which are individual sensor signals in the three axial directions (that is, components of an acceleration vector decomposed in the three axial directions) are subjected to square-mean operations, and absolute values of vectors are thereby obtained. To obtain the absolute values, at least two operational amplifiers are required for a squaring operation; therefore, at least six operational amplifiers are required for the operations for the three axial directions. In addition, operational amplifiers are also required for square-root operations. Therefore, with operational amplifiers for amplifying the sensor signals being included, totally, at least ten operational amplifiers are required. The need for so many operational amplifiers requires a circuit that has a complicated and expensive configuration that increases power consumption.
Under these circumstances, there is a demand for a cheap circuit capable of converting analog signals to absolute values, thereby generating digital signals of TTL and the like with a small amount of power consumption.
In view of the above-described problems, an object of the present invention is to provide a vector-signal processing circuit that allows power consumption to be reduced, and in addition, that allows configuration to be performed at low costs.
As shown in FIG. 2, even when current is allowed to pass forward, a diode causes a forward-voltage fall Vf, for example, in a range of 0.3 V to 0.5 V. Making use of this characteristic, the inventor exerted efforts to solve the above-described problems. As a result, it was found that digital-voltage-output signals of TTL and the like, which are equivalent to the square mean value, can be obtained by using diode bridges in full-wave-rectifier circuits, simply by selecting a combination of the forward-voltage fall and a reference voltage used as a threshold for comparison of a comparator, and by performing simple-addition of absolute values of the signals in the three axial directions.
To these ends, according to the present invention, there is provided a vector-signal processing circuit comprising a plurality of full-wave-rectifier circuits for individually rectifying analog signals made of at least two axial components of a vector signal, which are perpendicular to each other. It also comprises an adder circuit for adding outputs of the plurality of full-wave-rectifier circuits, and a comparator for converting outputs of the adder circuit. Each of the full-wave-rectifier circuits is composed of a diode bridge formed of diodes each having specific forward-voltage-falling characteristics, thereby converting the signals processed by the adder circuit to pseudo-absolute-value signals of the vector signal.
In the above an arrangement may be such that the analog signals are three axial components, the forward-voltage fall amount of the diode of three diode-bridge full-wave-rectifier circuits for rectifying the analog signals is substantially 0.3 V, and a threshold of the comparator is substantially 0.6 V.
According to the present invention summarized above, absolute-value outputs of the vector signal composed of very small analog signals in the three axial directions can be generated by using the circuit that can be operated with low power consumption and that can be produced cheaply. The absolute-value outputs can be generated by selection of forward-voltage-falling characteristics of the diodes that form the rectifier circuits, for example, by using only four operational amplifiers, without using an analog-digital converter or a microcomputer.